High density fuels are synthesized liquid hydrocarbon compounds, and in essence, the fuels, the same as hydrocarbon fuels refined from petroleum (e.g., aviation kerosene Jet A and rocket kerosene RP-1) can be applied in all air-inhaling engines and rocket engines that use kerosene as fuels. As compared with fuels refined from petroleum, the density of high density fuels increases to a great extent while the mass combustion calorific value is substantially equivalent thereto. Hence, this kind of fuels also can be called as high energy density fuels, and the volume calorific value of the fuels significantly increases. Thus, in the case of a specified volume of oil tanks, the fuels can provide more propulsion power, thereby to significantly increase voyage range or loading ability of aircrafts.
All high density liquid hydrocarbon fuels, e.g., RJ-4, RJ-5, JP-10, are synthesized by Diels-alder addition and hydrogenation with dicyclopentadienyl compounds and acetylene as starting materials. These fuels are derived from fossil resources, including petroleum, coal and the like. Biomass raw materials are also can be used for the preparation of high density fuels. Biomass resources can also be used to prepare high density fuel, wherein the most widely existing biomass resources is lignocellulose, and the lignocellulose derived compounds may be selected from the group consisting of phenol, anisole, guaiacol, cyclohexanone, cyclopentanone, acetone, γ-valerolactone and furfural. Now, high density fuels as prepared by these lignocellulose derived compounds primarily include long chain alkanes, while the synthesized polycyclic hydrocarbon compounds are less. In Green Chemistry 2015, 17 (8), 4473-4481, cyclohexanone is used to prepare composite fuels having a density of 0.887 g/ml. In Scientific Reports 5, Article number: 9565 (2015), cyclopentanol is used to prepare fuels having a density of 0.91 g/ml.
Perhydrofluorene is a tricyclic hydrocarbon compound having a density of up to 1.012 g/ml at 20° C., and thus it can be used as an additive to oil products to increase the density of the oil products. The current process for synthesis of perhydrofluorene is accomplished by reducing fluorene, and the fluorene is prepared by alkylation of benzene and methane dichloride or by intramolecular cyclization of halogen or boric acid-containing diphenyl methane derivatives. Patent EP0911309A1 proposes the scheme that a metal is loaded on an oxide support to convert diphenyl methane derivatives into fluorene-based compounds; the document, Angew. Chem. Int. Ed. 2012, 51, 5359-5362, uses an organic noble metal catalyst to catalyze the dehydrogenation cyclization of diphenyl methane derivatives to produce fluorene; the documents, Angew. Chem. Int. Ed. 2012, 51, 5359-5362; Org. Lett., Vol. 11, No. 20, 2009; J. AM. CHEM. SOC. 9 VOL. 130, NO. 48, 2008, 16159; and Adv. Synth. Catal. 2010, 352, 3267-3274, use a palladium-based catalyst to catalyze the intramolecular cyclization of halogen-containing aromatic hydrocarbons to prepare fluorene-based compounds. The hydrogenation of fluorene into perhydrofluorene is a relatively difficult process. Patent CN102701897A discloses that in a method for preparing cyclic hydrocarbon compounds by hydrogenation of washing oil fraction, at most 32.8% by weight of fluorene can be produced, and the selectivity of the perhydrofluorene only can reach 28.8%. The document, Chem. Eur. J. 2009, 15, 6953-6963, discloses that the yield of the hydrogenation of fluorene into perhydrofluorene only can reach 80% under the conditions of isopropanol as the solvent, RH/C as the catalyst, and hydrogen gas pressure of 5 MPa.
The current process for preparing perhydrofluorene or alkyl-substituted perhydrofluorene is to hydrogenate fluorene or alkyl-substituted fluorene. Fluorene may be derived from the following two sources: first, the fluorene may be prepared from coal tar; high temperature coal tar contains about 1.0 to 2.0% of fluorene, and after cooling, crystallization, and centrifugal separation, it can produce crude fluorene; thereafter, industrial fluorene is dissolved in benzene; after being neutralized and washed with water and solvent removal, the resultant fluorene is re-distilled, and the resultant distillate is recrystallized from gasoline and ethanol to produce fluorene with 95% purity, this method will consume a large quantity of energy; second, the fluorene may be prepared by intramolecular or intermolecular alkylation of halogen or boric acid-containing bicyclic aromatic hydrocarbons, for example, Angewandte Chemie International Edition 2012, 51 (22), 5359-5362 uses the metal Ru to activate the C—H bond of 2,2-diphenylacetic acid to produce fluorene by cyclization; Angewandte Chemie International Edition 2010, 49 (16), 2909-2912 uses Ru to catalyze the crosslinked coupling and intramolecular cyclization of 1,2-dihalobenzene and phenylboric acid to produce fluorene; Advanced Synthesis & Catalysis 2010, 352 (18), 3267-3274 uses palladium to catalyze the intramolecular alkylation of 2-halo-2′-methyl-1,1′-biphenyl to produce fluorene; however, this method has a high cost, and thus it is difficulty industrialized. A process for large-scale production of fluorene is provided that under the catalytic action of aluminum trichloride, methane dichloride and benzene or biphenyl can carry out an alkylation reaction. However, this process will have the following defects: the introduction of toxic benzene, difficult separation and recovery of introduced halogen, high production cost, heavy environmental pollutions, and meanwhile rigorous conditions for reducing fluorene derivatives and a low yield.